Calcium channels in smooth muscle cells from cerebral precapillary arterioles activate at more negative potentials than those from basilar artery

Abstract

We compared Ca2+ channels in cell-attached patches of smooth muscle cells from cerebral precapillary arterioles and basilar artery of guinea pig. Patches were studied without Ca2+ channel activators in the pipette solution. In both preparations, a 23 pS channel (40 mM Ba2+) sensitive to block by nifedipine was identified. In arteriolar but not in basilar artery patches, channel activity was recorded without apparent inactivation at potentials of -40 to -20 mV. Values for the number of channels in a patch x probability of channel opening (n.Po) at various potentials were fit to a Boltzmann function. For the arteriolar patches (n = 5) and for patches from basilar artery (n = 5), the midpoint potentials for the voltage dependence of n.Po were -9.3 mV and +8.9 mV, and maximum values of n.Po at positive potentials were 1.23 and 0.33. At potentials > or = 0 mV, the average for the maximum number of superimposed openings in basilar artery patches was 1.7 (n = 17) and in arteriolar patches was 6.5 (n = 6). For both preparations, histograms of channel open times at -10 mV required two time constants, 0.48 and 3.95 ms, and the shorter open state accounted for 88% of openings. Our data indicate that Ca2+ channel activity is likely to be more prominent near resting membrane potentials in arteriolar cells than in basilar artery cells.